Restoring a HP9830B calculator.

[Tony Duell]

Unfortunately (for the purposes of seeing if it works) the HP9866 manual feed (LOAD button, etc) uses its own clock oscillator to feed the motor step circuitry, and doesn't use the microcode/state machine. Loading data and printing, of course, is controlled by the microcode

The 2 main boards of logic are the ones on the far left side, and they are close together. But the microcode addess is available on one of the top test connectors. Seeing what the microcode does when you send it characters is a very good way to see what is, and is not, working.

As for swapping boards, I disagree that it is even a quick way of finding the faulty board. I've been caught (in my younger and more foolish days) by a case where a marginal problem on one board let it work with only some other boards. But all said 'other boards' were, in fact, working correctly and in-spec. So be careful.

The I/O board for the processor is, of course, a 16 bit shift register and the I/O flag logic. I've had problems with both areas.